Simplify the following expression: $4\sqrt{117}$.
Explanation: First, try to factor a perfect square out of the radical. $= 4\sqrt{117}$ $= 4\sqrt{9 \cdot 13}$ Separate the radical and simplify. $= 4\sqrt{9} \cdot \sqrt{13}$ $= 4 \cdot 3 \cdot \sqrt{13}$ $= 12\sqrt{13}$